In recent years, a mobile communication system of a W-CDMA (Wideband-Code Division Multiple Access) scheme based on the Code Division Multiple Access (CDMA) technique or a mobile communication system called UMTS (Universal Mobile Telecommunication System) has been proposed and specified by 3GPP (3rd Generation Partnership Projects).
Here, a mobile communication system of the W-CDMA scheme will be described with reference to FIG. 11 and FIG. 12.
As shown in FIG. 11, the mobile communication system of the W-CDMA scheme includes a mobile station UE (User Equipment), radio base stations NodeB, radio control station RNC (Radio Network Controller), and an exchange MSC/SGSN (Mobile Switching Center/Serving GPRS Support Node) and thereby forms a mobile communication system of a cellular scheme. A unit of control of this cellular scheme is an area called a “cell”.
Note that, although multiple exchanges MSC/SGSN are usually provided and are connected to one another in the above-described mobile communication system, a single exchange MSC/SGSN is illustrated in the example in FIG. 11 for the purpose of simplification.
Meanwhile, it is usual to provide the above-described mobile communication system with an apparatus called a home memory for storing subscriber information separately from the exchange. However, in the example in FIG. 11, functions of the home memory are assumed to be included in the exchange MSC/SGSN for the purpose of simplification.
Furthermore, introduction of a radio base station (a femto radio base station) for covering a narrow area such as an indoor area has advanced in recent years aside from a radio base station (a public radio base station) for covering a wide area such as an outdoor area.
As shown in FIG. 11, cells which are under the control of public radio base stations (radio base stations NodeB02 and NodeB02) are called as “macro cells (01, 02)” and a cell which is under the control of a femto radio base station (the femto radio base station NodeB03) is called as a “femto cell (03)”.
Specifically, a private area (an area formed by one or more femto cells) for a specific mobile station UE is formed by locating femto radio base stations in a standard home, a small office or the like and applying an inexpensive home IP line for connection with a radio control station RNC. In that area, provision of “user-dedicated services” including, application of a charging system for the femto cell and offering of additional functions exclusive to the femto cell to the specific mobile station UE, have been studied.
In the mobile communication system of the W-CDMA scheme, a mobile station UE which is turned on but not performing communication, i.e., in a “standby state” of standing by for a calling operation attributable to a terminal operation by a user or for call reception of an incoming call, is configured to measure received power of a pilot signal sent out in each cell by the radio base station NodeB via a CPICH (Common Pilot Channel) and to select the optimum pilot signal (i.e., the cell corresponding to the optimum pilot signal) autonomously. Explanation of such a selection algorithm will be omitted herein.
The mobile station UE is configured to stand by in the cell when the mobile station UE has selected the optimum pilot signal (i.e., the cell corresponding to the optimum pilot signal). In this case, the mobile station UE is configured to execute location registration processing with that cell.
An operation of the location registration processing in a related art will be described with reference to FIG. 12.
In step S5001, the mobile station UE compares a location number of a cell included in notification information of a selected femto cell 03 with a location number of a cell stored in the mobile station UE.
When both of the numbers coincide with each other, the mobile station UE terminates this operation and continues to stand by in the femto cell 03.
On the other hand, if both of the numbers do not coincide with each other, the mobile station UE sets up a radio line with a radio control station RNC by transmitting a “RRC Connection Request message” to the radio control station RNC in steps S5002 and S5003, and then transmits a “Routing Area Update Request message (a location registration request)” to request the location registration processing concerning a location registration area (a paging area) including the selected femto cell 03 to the exchange MSC/SGSN in step S5004.
After authentication processing concerning the mobile station UE is executed in step S5005, the exchange MSC/SGSN makes reference to an access list and determines whether or not the mobile station UE is allowed to access to the femto cell 03 (the femto radio base station NodeB03) in step S5006.
In the example in FIG. 12, the mobile station UE is assumed to not be allowed to access to the femto cell 03 (the femto radio base station NodeB03). Hence the exchange MSC/SGSN transmits a “Routing Area Update Reject message (a location registration rejection response)” to the mobile station UE in step S5007.
The exchange MSC/SGSN transmits an “IU Release Command message” to the radio control station RNC in step S5008, and the radio line between the radio control station RNC and the mobile station UE is released in step S5009.
The mobile station UE rejected for the location registration processing as described above cannot enter the aforementioned standby state, and the operation in FIG. 12 will be repeated if the mobile station UE measures the received power of the pilot signal sent out in each cell via the CPICH again after a lapse of a predetermined time period and reselects the same femto cell 03 as the cell corresponding to the optimum pilot signal.
However, according to the conventional mobile communication system, there is a problem that the mobile station UE which is unable to enter the standby state in the femto cell 03 cannot enjoy a communication service in the vicinity of the femto cell 03.
Moreover, according to the conventional mobile communication system, there is another problem of concern to waste a battery of the mobile station UE because the cell selection processing and the location registration processing are repeated.